Process for making pressure sensitive record materials



Patented Apr. 10, 1951 PROCESS FOR MAKING PRESSURE SENSI- TIVE RECORD MATERIALS Barrett K. Green and Robert W. Sandberg, Dayton, Ohio, assignors to The National Cash Register Company, Dayton, Ohio, a corporation of Maryland No Drawing. Application July 13, 1948, Serial No. 38,548

47 Claims. (01. 117-36) This invention relates to a process for making pressure-sensitive record material, and more particularly pertains to such material having minute particles of two kinds of substances which are color reactive on contact, one of the substances being in liquid form and the other" being in solid form, the particles of the two substances being arranged in proximity in profuse numbers but insulated from contact by material rupturable when pressure is applied, which pressure acts to bring the two kinds of substances together at the points of rupture to produce a distinctively colored localized mark.

The record material made by the process of this invention, although adapted for response to stylus pressures, is particularly adapted for response to pressures applied in impact printing operations such as by the striking or pressing sensitive to pressures caused by drawing a stylus thereover than to pressures derived from the impact of type. This novel record material also is an;-

improvement over that record material disclosed in United States Letters Patent No. 2,229,693, patg ented on October 20, 1942, on the application of Barrett K. Green. That patent discloses pressure-sensitive record material, especially adapted:

for impact work, such material including a rupturable insulating medium in which are interspersed liquid droplets of two kinds which react on contact to form color. The liquid droplets inan ionizing medium, glycerine, which reacted to produce color on contact by interchange of ions.

' Any such liquid ionizing medium available for use in such a system is hygroscopic making the rec- The process of the present invention provides I a record material with exceptional response to impact pressures and one having remarkable stability as no ionizing liquid is required. The

eluded solid color-forming materials dissolved in;

ord material unduly sensitive to moisture. I

liquid used to dissolve the active color ingredient 1 in the liquid reactant substance is a non-ionizing inert oily type of material which is non-hygroscopic and is used solely to dissolve the active ingredient and to obtain easier release and greater mobility of the droplets, when the supporting film is ruptured. Because of the mobility of the re leased liquid droplets at points of rupture of the insulating medium the new record material is highly sensitive both to drawing and to impact pressures yet it is resistant to destructive influences encountered in ordinary environment and normal handling operations. Thus, the new rec' 0rd material combines the best characteristics of known pressure responsive record materials by providing a novel liquid-solid reactant structure.

The principal object of the invention is to provide process for making a pressure-sensitiveiecord material on which a mark of distinctive color may be produced by the mere application of localized pressure, said material including colorforming substances of two kinds, one being solid and the other being liquid, the two substances normally being held insulated from reaction contact by a rupturable insulating medium until mark,- ing pressures rupture the insulating medium at points of pressure to bring about local contact of the two substances to produce a mark.

Another object of the invention is to provide a process for making such a record material in which one of the color reactant substances is dissolved in a non-ionizing oily liquid which may be dispersed as droplets in a rupturable solid insulating film so as to be readily available and mobile locally to make contact with the'other solid reactant'material when. released, by rupture of the film. v

Another object of the invention is toprovide a process for making such "a record material which is highly sensitive to impact pressures such as are met with in-typewriter or letter press work and for this effectthe two color reactants are arranged in separate overlying layers on-a web so that marking pressures vertical applied to the said layers will cause penetration of the color reactant substance of of the other layer. g 1

Further objects and objects relating; to details and economies of the process, will definitely appear from the detailed description to follow.- The objects of this invention have been attainedby the several embodiments thereof described in detail in the following specification. The invention is clearly defined and pointed out in the appended claims.

In the preferred form of this invention the liquid droplets of color reactant are dispersed in a film-forming substance which is applied as-a coating to a paper web and dried thereon leaving the liquid droplets entrapped therein. The solid color reactant particles, acting as adsorbents, are likewise dispersed in a film-forming substance which is applied as a second overlying coating. Both films are rupturable to force th reactant substances together.

Of the reactant materials employed, the liquid droplets contain an organic substance which is an electron donor aromatic compound having a double bond system which is converted to a more highly polarized conjugated 'form upon taking one layer into that part in an electron donor-acceptor adsorption chemical reaction, giving it a distinctive color, and the solid particles are of an inorganic substance which is an acid relative to the organic substance so as to be an electron acceptor when in adsorption contact therewith. The solid material is in fine particle formin order to furnish a large reactant surface per unit area of the record material, which enhances the depth of color produced in the record material.

The film-forming substances are derived from hydrophilic colloid materials that form pressure-rupturable films.

Although in the preferred form of the invention a single kind of solid reactant particle substance is used, such as Attapulgus clay, or attapulgite, it is within the scope of the invention to mix two or more kinds of solid reactants together, such as magnesium trisilicate and attapulgite, or to mix attapulgite with sodium aluminum silicate zeolites, which together act as adsorbents upon which color reactant adsorbates dissolved in the liquid droplets may be adsorbed.

Likewise the adsorbate substance may include one or more kinds of reactant such as crystal violet lactone, which i 3,3 bis(p-dimethylaminophenyl) -6-dirnethylaminophthalide, and tetrachloro malachite green lactone mixed together and dissolved in the Oily liquid.

The web used as a support may be paper or other material suitable as a record base. For instance, either cardboard, glass, metal or wood may be used if desired. The total thickness of the pressure-sensitive film need be no greater than from .001 to .002 of an inch so it may be supported on very thin paper stock. By placing a number of such thin-coated paper sheets in superimposed relation in a typewriter a number of printed copies of typewritten material may be made without the use of a typewriter ink ribbon or carbon manifold paper as is now the common practice.

As it is difficult, if not impossible, to show the exact structure of this coating by use of a drawing none accompanies this specification.

In the following examples, there will be described embodiments of this invention by which the objects of the invention have been successfully attained.

Example 1.--'I'he following embodiment of this invention constitutes the best mode of applying the principles thereof as contemplated up to the present time and may be considered the preferred embodiment. It comprises a base Web of paper, or the like, on one surface of which two coatings are applied, the first or undercoating being an insulating film in which are entrapped a profuse number of liquid droplets in which a color reactant substance is dissolved. These droplets are,

on the average, of the order of from 1 to 5 microns in diameter and are spaced apart, on the average, a distance of the order of /2 micron. The preferred thickness of this first coating, when dry, is of the order of .001 of an inch.

The first coating is made by dissolving one part by Weight of animal gelatin, having an isoelectric point of pH 8 and a jelly strength of 2'75 grams as measured by the Bloom gelometer, with three parts by weight of water heated to 150 Fahrenheit. 7

Into four parts by weight of the gelatin solution there is dispersed, or emulsified, three parts by weight of a solution of crystal violet lactone in chlorinated diphenyl.

4 l is 3,3 bis(p dimethylaminophenyl) -6-dimethylamino phthalide, in chlorinated diphenyl is made by dissolving three parts by weight of the crystal violet lactone in ninety-seven parts by weight of the chlorinated diphenyl which has a chlorine content averaging 48 per cent by weight. This chlorinated diphenyl solution is heated to the temperature of the gelatin solution before it is added thereto and emulsified.

The emulsion is applied while still hot, or if allowed to 0001 after reheating to and is dried either under normal atmospheric conditions or by artificial means such as a hot air blast or on a heated drying drum such as is commonly used in paper coating machines. It is considered that drying under normal atmospheric environment gives a somewhat better water resistance to the dried film or coating in which the chlorinated diphenyl solution droplets are entrapped.

The dried undercoating is next treated to drive the droplets out of the top surface layer and into the interior of the film so as, in effect, to form an impermeable surface skin thereon. This is accomplished by wetting the surface with water at room temperature, that is from 70-80 Fahrenheit, which water has had added thereto 1 per cent by weight of formaldehyde and 0.1 per cent by weight of a wetting agent such as dioctyl ester of sodium sulfosuccinate. The wetting should be allowed to persist for several minutes and thereafter the film is dried in a low humidity atmosphere. The surface wetting may be accomplished by floating the coated paper on the water, coated face down, or by carrying it on a partially submerged drum with the coated surface facing outwardly. The formaldehyde may be omitted, if desired.

The second, or overcoating, then is applied to the dried undercoating. In making the second coating 20 per cent, by weight, of paper coating starch in water is cooked at 200 Fahrenheit for 15 minutes and cooled to room temperature. Separately, 1 part by weight of attapulgite is dispersed in three parts by weight of water by use of a ball mill or equivalent. Four parts, by weight, of the attapulgite dispersion is mixed with one part, by weight, of the starch solution. The resultant mixture is applied, at room temperature, as an overcoating to the prepared paper having the gelatin coating dried thereon. This starch-clay overcoating is applied in any convenient manner, as by a paper coating machine. This overcoating when dry should have a thickness of the order of .0005 of an inch.

The thickness of the undercoating and the overcoating may .be varied somewhat without interferring greatly with the sensitivity of the material, such variation range being of the order of 25 per cent in either direction.

This record material when finished has a substantially white appearance and produces a dark blue mark which sharply defines the area of pressure or impact.

The impact of a marking instrument on the surface of this record material locally releases the oily droplets from the gelatin film and forces them into contact with the overlying attapulgite particles. The needle-like crystal aggregate structure of attapulgite prevents any substantial masking of it by the starch binder, thus leaving the attapulgite available to adsorb the color reactant crystal violet lactone from the released oil. Therefore, in this coating system the attapulgite solid particles are held in a non- This solution of crystal violet lactone. Whisk; 3:15 mas g on-insu at n binder Whereas the oil carried other reactant is protected as entrapped droplets in the gelatin insulating film.

The compound crystal violet lactone has the structure and the process of making it is described in United States Letters Patent No. 2,417,897, issued March 25, 1947, on the application of Clyde S. Adams, filed June 16', 1945, although the compound is incorrectly named in said patent as 3,3 bis(4-dimethylaminophenyl) 6 dimethylaminophenyl phthalide. An application for reissue of said patent is now pending.

While not nearly as good as the arrangement of the layers or films just described, it is within the broad aspects of the invention to apply the adsorbent-bearing film or coating first on the paper and next to apply the crystal violet lactone-bearing film as an overcoating.

Example .2.Another embodiment of the invention is the use of malachite green lactone, that is to say 3,3 bis(p-dimethylaminophenyl) phthalide, having the structure in place of the crystal violet lactone of Example 1 and in the same amount. This gives a substantially white record material producing a green mark when the pressure is applied. This green color is not as intense as the blue given by crystal violet lactone.

Example 3.Another embodiment of the invention is the use of tetrachloro malachite green lactone, that is to say 3,3 bis(p-dimethylaminophenyl) 4,5,6}? tetrachloro phthalide, having the structure in place of the crystal violet lactone of Example 1 and in the same amount. This gives a substantially white record material producing a green mark when pressure is applied.

Example 4.Another embodiment of the invention is the use of 3,3 bis(p-diethylaminophenyl)-G-dimethylamino phthalide, having the structure in place of the crysta1 violet lactone of Example 1 but using only one-sixth as much by weight. The normal color of this record material is dark yellow and upon pressure being applied it turns to a bluish gray.

In Examples 1 to 4 inclusive the attapulgite can be replaced with a synthetic zeolite material of the sodium aluminum silicate type preferably having a maximum particle size of 10 microns and used in essentially the same amount by weight as specified in Example 1 for the attapulgite. For use with the zeolite type of adsorbent, gelatin, methyl cellulose, polyvinyl alcohol, and casein may be substituted for the starch of Example 1 as a binder.

In Examples 1 to 5 inclusive, whether attapulgite or the sodium zeolite is used, there may be substituted for the starch a mixture of starch, casein, and a synthetic latex made of butadienestyrene copolymer material. when dried with the attapulgite or zeolite material therein, the amount of starch should be 7 per cent, the amount of casein should be 1 per cent, and the amount of latex should be 7 per cent all by Weight with respect to the weight of the attapulgite or zeolite material. In making such a binder a starch solution is made as described in Example 1 and allowed to cool. Next one part of casein is dispersed in two parts of cold Water, by weight, and allowed to swell for one-half hour,

. after which seven more parts of cold water and water contains 0.2% of sodium pyrophosphate.

To 10 parts by weight of the dispersed adsorbent, eliminating the weight of the water, is added 3.5 parts by weight of the starch solution, 1.6 parts by weight of the latex, and 1 part by Weight of the casein solution. This binder material is characterized by greater adhesion to the adjacent In such a binder.

coating and by excellent properties as far as the access of the adsorbent material to the action of the liquid color reactant droplets is concerned.

In Examples 1 to 5 the attapulgite may be replaced with an equivalent amount of halloysite,

and in Examples lto 4 the attapulgite may be replaced by an equivalent amount of magnesium trisilicate. Mixtures of the adsorbents will do as well as the individual adsorbents.

With respect to the zeolite material the sodium of the specified sodium aluminum silicate may be replaced with other cations such as nickel, copper, iron, zinc, mercury, barium, lea-d, cadmium and potassium to give zeolites with equivalent or better color reactant qualities.

The exchangeable calcium cations on natural attapulgite may be replaced by other cations to give workable adsorbents in the same way as noted for the zeolites. In addition hydrogen may be substituted for the calcium exchange cations of attapulgite.

The adsorbent material should be accessible to the liquid droplets containing the color reactant material to be adsorbed thereon and the action of the coating binder tends to mask the exterior surface available on such adsorbent particles. The needle-like aggregates of attapulgite and the porous structure of zeolites, contain interiorly active surfaces, not masked by the binder, which are left available for adsorbing the color reactant in the liquid droplets and, hence, these types of adsorbent are particularly suited for the novel structure which is the subject of this invention. I-Ialloysite and magnesium trisilicate seem to be of such structure as has available interior adsorbent surfaces and therefore are given as substitute materials to act as the adsorbent material of the system.

The pressure-sensitive record material made by the process as disclosed herein is disclosed and claimed in the copending application of Barrett K, Green and Robert W. Sandberg, Serial No. 38,547, filed July 13, 1948.

It is understood that the processe for making pressure-sensitive record material described herein are susceptible of considerable variations without departing from the spirit of the invention.

What is claimed is:

l. The method of making a pressure-sensitive record material containing a liquid substance and a solid substance reactive on contact to produce a mark of distinctive color, including the steps of first coating a web with an emulsion having as the internal discontinuous phase the liquid reactant substance and having as the external continuous phase a substance dryable to a solid film which entraps the internal phase as liquid droplets; drying said film; treating the surface of the film to form a surface skin; applying a film-like overcoatin to the exposed surface of the first coating said overcoating including a liquid film-forming binder dryable to a solid condition and said overcoating having profusely dispersed therein particles of the solid color-forming reacting substance, the liquid substance including an electron donor aromatic organic compound having a double bond system which is convertible to a more highly polarized conjugated form upon taking part in an electron donor-acceptor adsorption chemical reaction, giving it a distinctive color, and the solid substance being an inorganic material in fine particle form providing a large adsorbent surface area and said inorganic material being an acid relative to the organic compound and acting as an adsorbent therefor 4. The method of claim 2 in which the dissolved color reactant is 33 bis(p-diethylaminophenyl)-fi-dimethylamino phthalide having the structure (C2115) zN- (C2 5) 2 5. The method of claim 2 in which the dissolved color reactant is 3,3 bis(p-dimethylaminophenyl) phthalide having the structure 6. The method of claim 2 is which the dissolved color reactant is 3,3 bis(p-dimethylaminophenyl) 4,5,6}? tetrachloro phthalide having the structure 7. The method of claim 2 in which the dissolved color reactant is 2,4 bislp-(p-dimethylaminoazo) ani1ino]-6-,-hydroxy sym. triazine having the structure 8. The method of claim 2 in which the oily solvent is a chlorinated diphenyl material.

9. The method of claim 8 in which the chlorinated diphenyl material has a chlorine content of approximately 48 per cent by weight.

10. The method of claim 1 in which the continuous phase of the emulsion is gelatin.

11. The method of claim 1 in which the web is paper. 7

12. The method of claim 1 in which the solid color reactant substance is attapulgite.

13. The method of claim 12 in which the solid color reactant substance attapulgite is held in a starch binding film.

14. The method of claim 1 in which the solid color reactant substance is dispersed in fine particle form in a starch binder material in a dryable liquid and coated over the film containing the liquid droplets.

15. The method of making a pressure-sensitive record material containing a liquid substance and a solid substance reactive on contact to produce a mark of distinctive color including the steps of preparing an emulsion having a continuous gelatin phase and a discontinuous phase of an inert oily substance in which is dissolved a color reactant substance to form the liquid color reactant 10 is starch and the color reactant solid is atta= pulgite. k

23. The method of claim 15 in which the color reactant solid is attapulgite.

24. The method of claim 15 in which the color reactant substance in the liquid droplets is 3,3- bis(p-dimethylaminophenyl) 6 dimethylamino phthalide having the structure (CHmN more):

( 2 5) 2 N a a) 2 substance; the step of coating the emulsion on a web and drying the coating so the gelatin will form a solid film in which the discontinuous phase of the emlusion persists as liquid droplets; treating the surface of the film to form a surface skin; the step of preparing a dispersion of particles of the solid color reactant in a dryable a distinctive color, and the solid substance being an inorganic material in fine particle form providing a large adsorbent surface area and said inorganic material being an acid relative to the organic compound and acting as an adsorbent therefor so as to be an electron acceptor when the organic compound is in adsorption contact therewith.

16. The method of claim 15 in which the web is paper.

17. The method of claim 15 in which the inert oily substance is a chlorinated diphenyl material.

18-. The method of claim 17 in which the chlorinated diphenyl material has a chlorine content of approximately 48 per cent.

19. The method of claim 15 in which the dried gelatin film is wet on the surface with water and quickly dried.

20. The method of claim 19 in which the water contains a slight amount of formaldehyde.

21. The method of claim 15 in which the binder is starch.

22. The method of claim 15 in which the binder N(C a)2 26. The method of claim 15 in which the color reactant substance in the liquid droplets is 3,3 bis(p-dimethylaminophenyl) phthalide having the structure 27. The method of claim 15 in which the dissolved color reactant is 3,3 bis(p-dimethylaminophenyl) 4,5,6}? tetrachloro phthalide having the structure 28. The method of claim 15 in which the dissolved color reactant is 2,4 bis[p(p-dimethylii aminoazo) anilinol -6-hydroxy sym. triazine havmg the structure 29. The method of making a pressure-sensitive record material containing liquid droplets and solid particles which react on contact to produce a distinctively colored mark, including the steps of dissolving gelatin in water and dispersing therein an oily'substance in which is dissolved a color reactant substance so as to form an emulsion, the continuous gelatin phase of which is dryable to a solid; coating the emulsion in a thin film on a record material web; drying the gelatin film thus entrapping the dispersed phase as liquid droplets; treating the surface of the film to form a surface skin; dispersing the solid color reactant particles in a binder solution dryable to a solid; and coating a film of the binder material dispersion on top of the gelatin film and drying it, the color-reactant in the droplets in cludes an electron donor aromatic organic compound having a double bond system which is convertible to a more highly polarized conjugated form upon taking part in an electron donor-acceptor adsorption chemical reaction, giving it a distinctive color the solid particles being an inorganic substance of such fineness as to provide a large adsorbent surface area, and said inorganic substance being an acid relative to the organic compound so as to be an electron acceptor when in adsorption contact with said organic compound.

30. The method of claim 29 in which the surface of the dried gelatin film is treated with water and quickly dried, to drive the liquid droplets out of the top layer before the binder material dispersion is applied thereover.

31. The method of claim 29 in which the droplets average between-l and 5 microns in diameter.

32. The method of claim 29 in which the droplets are spaced apart on the average, a distance of A; micron.

33. The method of claim 29 in which the droplets average between 1 and 5 microns in diameter and are spaced apart, on the average, a distance of micron.

34. The method of claim 29 in which the thickness of the dried gelatin film is of the order of one thousandth of an inch.

35. The method of claim 29 in which the gelatin has an isoelectric point of approximately pH 8 and a jelly strength of approximately 275 grams as measured by the Bloom gelometer.

36. The method of claim 29 in which one part by weight of the gelatin is dissolved in three parts by weight of water.

37. The method of claim 36 in which four parts by weight of the gelatin-water solution are used with three parts by weight of a solution of three parts by weight of 3,3 bis'(p-dimethylaminophenyl) -6-dimethylamino phthalide in ninetyseven parts by weight chlorinated diphenyl of approximately 48 per cent chlorine by weight.

38. The method of claim 37 in which the material dissolved in the chlorinated diphenyl is 3,3 bis (p-diethylaminophenyl) -6-dimethylamino phthalide.

39. The method of claim 37 in which the material dissolved in the chlorinated diphenyl is 3,3 bis(p-dimethylaminophenyl) phthalide.

40. The method of claim 37 in which the material dissolved in the chlorinated diphenyl is 3,3 bis(p-dimethylaminophenyl) 4,5,6,7 tetrachloro phthalide.

41. The method of claim 37 in which the material dissolved in the chlorinated diphenyl is 2,4 bis [p-(p-dimethylaminoazo) an'ilinol-G- hydroxy sym. triazine.

42. The method of claim 29 in which the surface of the gelatin film after being dried to a solid is wet with water of -80 Fahrenheit and containing approximately 1 per cent of formaldehyde.

43. The method of claim 42 in which the water with which the surface of the gelatin is treated contains approximately V10 of a per cent of dioctyl ester of sodium sulfo'su'ccinate or its equivalent as a wetting agent.

44. The method of claim 29 in which the average size of the solid color reactant particles in the binder is of the order of 10 microns in diameter.

45. The method of claim 29 in which the binder solution for the solid particles comprises approximately 20 per cent by weight of paper coating starch in water cooked at 200 Fahrenheit for 15 minutes.

46. The method of claim 29 in which four parts by weight of a dispersion of one part by weight of the solid reactant material in three parts by weight of water is mixed with one part by weight of the starch binder solution.

47. The method of claim 29in which the coating containing the solid color reactant when dried, has a thickness of the order of .0005 of an inch.

- BARRETT K. GREEN.

ROBERT W. SANDBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNI'IED STATES PATENTS OTHER REFERENCES ,Hau ser et 2.1., Color Reactions Between Clays and Amines, July19 10, pgs. 1811-14. 

1. THE METHOD OF MAKING A PRESSURE-SENSITIVE RECORD MATERIAL CONTAINING A LIQUID SUBSTANCE AND A SOLID SUBSTANCE REACTIVE ON CONTACT TO PRODUCE A MARK OF DISTINCTIVE COLOR, INCLUDING THE STEPS OF FIRST COATING A WEB WITH AN EMULSION HAVING AS THE INTERNAL DISCONTINUOUS PHASE THE LIQUID REACTANT SUBSTANCE AND HAVING AS THE EXTERNAL CONTINUOUS PHASE A SUBSTANCE DRYABLE TO A SOLID FILM WHICH ENTRAPS THE INTERNAL PHASE AS LIQUID DROPLETS; DRYING SAID FILM; TREATING THE SURFACE OF THE FILM TO FORM A SURFACE SKIN; APPLYING A FILM-LIKE OVERCOATING TO THE EXPOSED SURFACE OF THE FIRST COATING SAID OVERCOATING INCLUDING A LIQUID FILM-FORMING BINDER DRYABLE TO A SOLID CONDITION AND SAID OVERCOATING HAVING PROFUSELY DISPERSED THEREIN PARTICLES OF THE SOLID COLOR-FORMING REACTING SUBSTANCE, THE LIQUID SUBSTANCE INCLUDING AN ELECTRON DONOR AROMATIC ORGANIC COMPOUND HAVING A DOUBLE BOND SYSTEM WHICH IS CONVERTIBLE TO A MORE HIGHLY POLARIZED CONJUGATED FORM UPON TAKING PART IN AN ELECTRON DONOR-ACCEPTOR ADSORPTION CHEMICAL REACTION, GIVING IT A DISTINCTIVE COLOR, AND THE SOLID SUBSTANCE BEING AN INORGANIC MATERIAL IN FINE PARTICLE FORM PROVIDING A LARGE ADSORBENT SURFACE AREA AND SAID INORGANIC MATERIAL BEING AN ACID RELATIVE TO THE ORGANIC COMPOUND AND ACTING AS AN ADSORBENT THEREFOR SO AS TO BE AN ELECTRON ACCEPTOR WHEN THE ORGANIC COMPOUND IS IN ADSORPTION CONTACT THEREWITH. 